of Radium and Uranium. 



Numerous unsuccessful attempts have been made to 

 reduce the specific a-ray activity of uranium. In one 

 experiment conducted by the authors about two kilo- 

 grams of pure uranium nitrate were subjected to frac- 

 tional crystallization and a least soluble "head" 

 fraction weighing about twenty grams was obtained 

 after about forty operations. The specific a-ray activity 

 of the uranium in this material did not vary by as much 

 as one per cent from the specific activity of the uranium 

 in the original nitrate. This shows that the two compo- 

 nents are so closely allied chemically as to be insepa- 

 rable, a conclusion which is supported by all the other 

 known facts at our disposal. 



We may outline, therefore, the progressive disintegra- 

 tion of the uranium atom, considering for the present 

 only the products emitting a-rays, as taking place in the 

 following manner: the parent element, uranium I, pro- 

 duces the product uranium II. This in turn produces 

 ionium, which disintegrates to form radium, followed 

 successively by radium emanation, radium A, radium C 

 and polonium. When these are all present in equili- 

 brium proportions, as is the case in a non-emanating, 

 old, radioactive mineral, then certain comparatively sim- 

 ple relations will exist between the a-ray activities of the 

 different constituents. It has been shown by Geiger 7 

 that the ionizing power of an a-particle is proportional 

 to the two-thirds power of its range. The ionization 

 produced by equal numbers of a-particles emitted by two 

 different radio-elements will therefore be proportional to 

 the two-thirds power of the ranges of these particles. In 

 a series of successive products in equilibrium, each prod- 

 uct emits the same number of a-particles in unit time. 

 The relative ionization (and therefore the relative activi- 

 ties) due to each of these products should therefore be 

 proportional to the two-thirds power of the range of the 

 respective a-particles. 



This relation has been shown 8 to hold quite closely in 

 the case of radio-thorium and its a-ray products, and 

 also in the actinium and the radium series of products. 

 The chief object of the work described in the present 

 paper was to apply the same methods to the case of the 



7 Proc. Boy. Soc, A 83, 505, 1910. 



8 McCoy and Viol, Phil. Mag., 25, 333, 1913 : McCoy and Leman, Phys. 

 Bev., 4, 409, 1914; ibid. 6, 185, 1915. 



